Ini_set(): headers already sent. you cannot change the session module's ini settings at this time

<?php
        class Mahasiswa extends CI_Controller {

	public function __construct(){
		parent:: __construct();
		$this->load->model('mod_mahasiswa');

	}

	public function index() {

			$data['record']=  $this->mod_mahasiswa->select_all()->result();
        $this->load->view('halaman_admin/v_admin',$data);
	}


    	public function simpan_data()
	{
		$this->mod_mahasiswa->simpan_data();
		$data['mhs'] = $this->mod_mahasiswaa->get_mhs();
		$data['c_mhs']  = $this->mod_mahasiswa->count_mahasiswa();
		$this->load->view('halaman_admin,v_admin',$data);
	}

    public function tambah(){
		$this ->load->view('halaman_admin/post_mhs');

	}
	public Function edit() {
        if (isset($_POST['submit'])) {
            $this->mod_mahasiswa->update();
            redirect('Mahasiswa');
        } else {
            $id = $this->uri->segment(4);
            $data['row'] = $this->db->get_where('Platform_Mobile', array('NIM' => $NIM))->row_array();
            $this->template->load('halaman_admin/edit', $data);
        }
    }

Public function delete(){
        $this->db->where('NIM');
        $this->db->delete('Platform_Mobile');
        redirect('Mahasiswa'); }

}
?>